Sperm telomere length in motile sperm selection techniques: A qFISH approach.

Several studies have associated telomere shortening with alterations in reproductive function. The objective of the present study was to determine telomere length (TL) in spermatozoa selected by either density-gradient centrifugation (DGC) or swim-up. The analysis of TL was performed using quantitative fluorescent in situ hybridisation (qFISH) using PNA probes in combination with a chromatin decompaction protocol in sperm cells. Results of TL were 24.64 ± 5.00 Kb and 24.95 ± 4.60 Kb before and after DGC, respectively, and 19.59 ± 8.02 Kb and 20.22 ± 5.18 Kb before and after swim-up respectively. Sperm selected by DGC or swim-up did not show any significant differences in TL as compared to nonselected sperm (p > .05). Negative correlations between TL and sperm motility (r = -.308; p = .049) and concentration (r = -.353; p = .028) were found. Furthermore, exposure of sperm to increasing concentrations of hydrogen peroxide during incubation resulted in a reduction in TL. These data indicate that oxidative stress may be one of the main factors involved in the reduction of TL in sperm. Preliminary clinical results from patients included in this study indicate that TL was shorter in spermatozoa from couples who never achieved a pregnancy compared to couples who did achieve at least one natural pregnancy (p < .05); however, the clinical utility of this biomarker still needs to be confirmed in further studies.

Nuclear degraded sperm subpopulation is affected by poor chromatin compaction and nuclease activity.

There is an interest in the nuclear degraded sperm subpopulation because, although it is present in a low percentage in all semen samples, patient groups such as varicocele and rearranged genome carriers show high levels of these degraded spermatozoa. This study is designed with two objectives in mind: first, incubations of H2 O2 and nuclease on DTT-treated and untreated samples to show the aetiology of this subpopulation and second, assessment of the correlation between the protamine ratio and nuclear degraded spermatozoa. A very high increase in the nuclear degraded subpopulation has been found with nuclease incubation, and it is even higher when it has been merged with nuclear decompaction using DTT. Alternatively, incubation with H2 O2 with and without DTT did not show such a significant increase in nuclear degraded spermatozoa. The protamine ratio correlated with this subpopulation, showing, in patients, that poor nuclear compaction would turn the sperm susceptible to degradation. Then, the assessment of nuclear degraded spermatozoa might not be only a measure of DNA degradation but also an indicator of chromatin compaction in the spermatozoa. Different patient groups would fit this model for sperm nuclear degradation, such as varicocele patients, who show a high percentage of immature spermatozoa and nuclear degraded spermatozoa, and reorganised genome carriers, where reorganisation might also cause poor chromatin compaction on the sperm nucleus.

Double-stranded DNA breaks hidden in the neutral Comet assay suggest a role of the sperm nuclear matrix in DNA integrity maintenance.

We used a mouse model in which sperm DNA damage was induced to understand the relationship of double-stranded DNA (dsDNA) breaks to sperm chromatin structure and to the Comet assay. Sperm chromatin fragmentation (SCF) produces dsDNA breaks located on the matrix attachment regions, between protamine toroids. In this model, epididymal sperm induced to undergo SCF can religate dsDNA breaks while vas deferens sperm cannot. Here, we demonstrated that the conventional neutral Comet assay underestimates the epididymal SCF breaks because the broken DNA ends remain attached to the nuclear matrix, causing the DNA to remain associated with the dispersion halo, and the Comet tails to be weak. Therefore, we term these hidden dsDNA breaks. When the Comet assay was modified to include an additional incubation with sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) after the conventional lysis, thereby solubilizing the nuclear matrix, the broken DNA was released from the matrix, which resulted in a reduction of the sperm head halo and an increase in the Comet tail length, exposing the hidden dsDNA breaks. Conversely, SCF-induced vas deferens sperm had small halos and long tails with the conventional neutral Comet assay, suggesting that the broken DNA ends were not tethered to the nuclear matrix. These results suggest that the attachment to the nuclear matrix is crucial for the religation of SCF-induced DNA breaks in sperm. Our data suggest that the neutral Comet assay identifies only dsDNA breaks that are released from the nuclear matrix and that the addition of an SDS treatment can reveal these hidden dsDNA breaks.

First successful double-factor PGD for Lynch syndrome: monogenic analysis and comprehensive aneuploidy screening.

Preimplantation genetic diagnosis (PGD) has been applied worldwide for a great variety of single-gene disorders over the last 20 years. The aim of this work was to perform a double-factor preimplantation genetic diagnosis (DF-PGD) protocol in a family at risk for Lynch syndrome. The family underwent a DF-PGD approach in which two blastomeres from each cleavage-stage embryo were biopsied and used for monogenic and comprehensive cytogenetic analysis, respectively. Fourteen embryos were biopsied for the monogenic disease and after multiple displacement amplification (MDA), 12 embryos were diagnosed; 5 being non-affected and 7 affected by the disease. Thirteen were biopsied to perform the aneuploidy screening by short-comparative genomic hybridization (CGH). The improved DF-PGD approach permitted the selection of not only healthy but also euploid embryos for transfer. This has been the first time a double analysis of embryos has been performed in a family affected by Lynch syndrome, resulting in the birth of two healthy children. The protocol described in this work offers a reliable alternative for single-gene disorder assessment together with a comprehensive aneuploidy screening of the embryos that may increase the chances of pregnancy and birth of transferred embryos.

Effects of oral antioxidant treatment upon the dynamics of human sperm DNA fragmentation and subpopulations of sperm with highly degraded DNA.

The primary aim of this study was to determine the effect of oral antioxidant treatment (1500 mg of l-Carnitine; 60 mg of vitamin C; 20 mg of coenzyme Q10; 10 mg of vitamin E; 10 mg of zinc; 200 µg of vitamin B9; 50 µg of selenium; 1 µg of vitamin B12) during a time period of 3 months upon the dynamics of sperm DNA fragmentation following varying periods of sperm storage (0 h, 2 h, 6 h, 8 h and 24 h) at 37 °C in a cohort of 20 infertile patients diagnosed with asthenoteratozoospermia. A secondary objective was to use the sperm chromatin dispersion test (SCD) to study antioxidant effects upon a specific subpopulation of highly DNA degraded sperm (DDS). Semen parameters and pregnancy rate (PR) were also determined. Results showed a significant improvement of DNA integrity at all incubation points (P < 0.01). The proportion of DDS was also significantly reduced (P < 0.05). Semen analysis data showed a significant increase in concentration, motility, vitality and morphology parameters. Our results suggest that antioxidant treatment improves sperm quality not only in terms of key seminal parameters and basal DNA damage, but also helps to maintain DNA integrity. Prior administration of antioxidants could therefore promote better outcomes following assisted reproductive techniques.

Alkaline and neutral Comet assay profiles of sperm DNA damage in clinical groups.

BACKGROUND: The analysis of sperm DNA fragmentation has become a new marker to predict male infertility, and many techniques have been developed. The sperm Comet assay offers the possibility of differentiating single- and double-stranded DNA (ssDNA and dsDNA) breaks, which could have different effects on fertility. The objective of this study was to perform a descriptive characterization of different groups of patients, such as those with asthenoteratozoospermic (ATZ) with or without varicocele, oligoasthenoteratozoospermic (OATZ) or balanced chromosome rearrangements, as compared with fertile donors. The Comet assay was used to investigate sperm samples for ssDNA and dsDNA breaks. METHODS AND RESULTS: The analysis of alkaline and neutral Comet assays in different groups of patients showed different sperm DNA damage profiles. Most fertile donors presented low values for ssDNA and dsDNA fragmentation (low-equivalent Comet profile), which would be the best prognosis for achieving a pregnancy. OATZ, ATZ and ATZ with varicocele presented high percentages of ssDNA and dsDNA fragmentation (high-equivalent Comet assay profile), ATZ with varicocele being associated with the worst prognosis, due to higher levels of DNA fragmentation. Rearranged chromosome carriers display a very high variability and, interestingly, two different profiles were seen: a high-equivalent Comet assay profile, which could be compatible with a bad prognosis, and a non-equivalent Comet assay profile, which has also been found in three fertile donors. CONCLUSIONS: Comet assay profiles, applied to different clinical groups, may be useful for determining prognosis in cases of male infertility.

Whole-chromosome aneuploidy analysis in human oocytes: focus on comparative genomic hybridization.

The study of aneuploidy in human oocytes, discarded from IVF cycles, has provided a better understanding of the incidence of aneuploidy of female origin and the responsible mechanisms. Comparative genomic hybridization (CGH) is an established technique that allows for the detection of aneuploidy in all chromosomes avoiding artifactual chromosome losses. In this review, results obtained using CGH in single cells (1PB and/or MII oocytes) are included. The results of oocyte aneuploidy rates obtained by CGH from discarded oocytes of IVF patients and of oocyte donors are summarized. Moreover, the mechanisms involved in the aneuploid events, e.g. whether alterations occurred due to first meiotic errors or germ-line mitotic errors are also discussed. Finally, the incidence of aneuploid oocyte production due to first meiotic errors and germ-line mitotic errors observed in oocytes coming from IVF patients and IVF oocyte donors was assessed.

Dynamics of sperm DNA fragmentation in patients carrying structurally rearranged chromosomes.

This investigation was conducted to assess the baseline level of sperm DNA fragmentation (SDF) in a cohort of patients presenting chromosomal rearrangements (nine reciprocal translocations and two inversions). In a separate experiment, a dynamic analysis to calculate the rate of SDF (rSDF), after a varying period of sperm storage (0 h, 1 h, 4 h, 8 h and 24 h) at 37 °C, was performed. Results were compared with eight fertile donors. Different experimental approaches to assess SDF, such as terminal transferase dUTP nick-end labelling (TUNEL), sperm chromatin structure assay (SCSA) and sperm chromatin dispersion test (SCDt), were used. No differences for the baseline level of SDF were found. Carriers of reorganized genomes showed statistically higher levels of SDF than did control donors (p = 0.025 for TUNEL; p = 0.022 for SCSA; p = 0.014 for SCDt). However, 54.5% (6/11) of the patients presented values similar to those of control donors. There was no significant difference in rSDF (p = 0.34). Nevertheless, the results suggest that a high variability for SDF and rSDF exists in these patients. Routine analysis of SDF and rSDF should be considered in patients presenting rearranged genomes to determine fertility status for assisted reproductive techniques (ART) purposes.

Sperm DNA integrity and meiotic behavior assessment in an infertile male carrier of a 9qh+++ polymorphism.

Although several reports on male infertility suggest a relationship between chromosome 9 polymorphisms and infertility, the effects on the phenotype have not been extensively reported. In this study, an infertile patient was found to carry a 9qh+++ chromosome. The flow cytometric TUNEL assay and SCD test have been applied to characterize sperm DNA integrity. In order to assess its meiotic behaviour, synapsis, recombination, and aneuploidy, analyses have been also performed. Sperm DNA fragmentation (SDF) was 77.81% and 87% for the TUNEL and SCD tests, respectively. Ninety-two percent of pachytene cells analyzed showed meiotic abnormalities. The mean number of MLH1 foci per pachytene in the control group was higher (49) than the mean found in the 9qh+++ patient (38) (P < .0001). In spermatozoa, significant increases of disomy rates were observed for chromosome 18 and for the sex chromosomes (P < .0001). These disturbances could be present in other male carriers of a less marked 9qh+.

Reliability of short comparative genomic hybridization in fibroblasts and blastomeres for a comprehensive aneuploidy screening: first clinical application.

BACKGROUND: Comparative genomic hybridization (CGH) is a valuable alternative to fluorescence in situ hybridization (FISH) for preimplantation genetic screening (PGS) because it allows full karyotype analysis. However, this approach requires the cryopreservation of biopsied embryos until results are available. The aim of this study is to reduce the hybridization period of CGH, in order to make this short-CGH technique suitable for PGS of Day-3 embryos, avoiding the cryopreservation step. METHODS: Thirty-two fibroblasts from six aneuploid cell lines (Coriell) and 48 blastomeres from 10 Day-4 embryos, discarded after PGS by FISH with 9 probes (9-chr-FISH), were analysed by short-CGH. A reanalysis by the standard 72 h-CGH and FISH using telomeric probes was performed when no concordant results between short-CGH and FISH diagnosis were observed. The short-CGH was subsequently applied in a clinical case of advanced maternal age. RESULTS: In 100% of the fibroblasts analysed, the characteristic aneuploidies of each cell line were detected by short-CGH. The results of the 48 blastomeres screened by short-CGH were supported by both 72 h-CGH results and FISH reanalysis. The chromosomes most frequently involved in aneuploidy were 22 and 16, but aneuploidies for the other chromosomes, excepting 1, 10 and 13, were also detected. Forty-one of the 94 aneuploid events observed (43.6%) corresponded to chromosomes which are not analysed by 9-chr-FISH. CONCLUSIONS: We have performed a preliminary validation of the short-CGH technique, including one clinical case, suggesting this approach may be applied to Day-3 aneuploidy analysis, thereby avoiding embryo cryopreservation and perhaps helping to improve implantation rate after PGS.

Studying meiosis: a review of FISH and M-FISH techniques used in the analysis of meiotic processes in humans.

It is well known that chromosome in situ hybridization allows the unequivocal identification of targeted human somatic chromosomes. Different fluorescent in situ hybridization (FISH) techniques have been developed throughout the years and, following the mitotic studies, meiotic analyses have been performed using these different techniques. The introduction of M-FISH techniques to the analysis of meiotic cells has allowed the study of meiotic processes for every individual human chromosome. In this paper, we review the different FISH and M-FISH techniques that have been used on human meiotic cells in both men and women.

The organisation and functioning of Veterinary Services: results of a 2005 survey of Member Countries of the World Organisation for Animal Health.

A questionnaire was sent to the 167 Member Countries of the World Organisation for Animal Health (OIE) in 2004 and 2005. The organisation and functioning of national Veterinary Services were analysed based on the responses from 85 of these countries. Leaving aside variations between countries, Veterinary Services are very involved in animal health and food safety controls at farm level (including animal feed), and during primary and secondary processing, whether alone or in conjunction with other services. At the lower end of the chain, namely distribution and the food service industry, responsibilities tend to be more widely shared. Veterinary Services have a central responsibility in international trade in animals and animal products. The main weaknesses in the chain of controls concern the logistical and financial resources of Veterinary Services, and insufficient involvement of livestock producers and even of field veterinarians. The many recent reforms are tending to provide a more consistent, integrated approach to animal health and food safety controls 'from the stable to the table'.

Spatial-temporal Variations of Bovine Tuberculosis Incidence in France between 1965 and 2000.

We analysed the spatiotemporal variations of bovine tuberculosis (bTB) incidence between 1965 and 2000 in France at the department level (95 areas). Using a Bayesian space-time model, we studied the association between the evolution of bTB incidence and changes of cattle population structure and of herd management practices. Several spatiotemporal hierarchical Bayesian models were compared, and the deviance information criterion was used to select the best of them. Southern France remained a high-risk area over the analysed period, whereas central and western regions were low-risk areas. Besides the frequency of tuberculin skin testing (fixed according to bTB incidence in the preceding years), four factors were associated with an increased risk of bTB: the average herd density and size, the percentage of dairy cows in the cattle population, and the percentage of permanent grassland in cultivated surfaces area. These four factors are linked to the progressive professionalization and specialization of cattle farming, with the disappearance of family farms and of the intensification of breeding systems (especially in dairy farms after the application of the milk quota system in the 1980s). Both trends probably played a significant role in reducing the risk of bTB in France between 1965 and 2000, besides mandatory detection and control procedures.

Frequency and distribution of chromosome abnormalities in human spermatozoa.

This study reviews the frequency and distribution of numerical and structural chromosomal abnormalities in spermatozoa from normal men obtained by the human-hamster system and by multicolor-FISH analysis on decondensed sperm nuclei. Results from large sperm karyotyping series analyzed by chromosome banding techniques and results from multicolor FISH in sperm nuclei (of at least 10(4) spermatozoa per donor and per probe) were reviewed in order to establish baseline values of the sperm chromosome abnormalities in normal men. In karyotyping studies, the mean disomy frequency in human sperm is 0.03% for each of the autosomes, and 0.11% for the sex chromosomes, lower than those reported in sperm nuclei by FISH studies using a similar methodology (0.09% and 0.26%, respectively). Both types of studies coincide in that chromosome 21 and sex chromosomes have a greater tendency to suffer segregation errors than the rest of the autosomes. The mean incidence of diploidy, only available from multicolor FISH in sperm nuclei, is 0.19%. Inter-donor differences observed for disomy and diploidy frequencies among FISH studies of decondensed sperm nuclei using a similar methodology could reflect real differences among normal men, but they could also reflect the subjective application of the scoring criteria among laboratories. The mean frequency of structural aberrations in sperm karyotypes is 6.6%, including all chromosome types of abnormalities. Chromosome 9 shows a high susceptibility to be broken and 50% of the breakpoints are located in 9q, between the centromere and the 9qh+ region. Structural chromosome aberrations for chromosomes 1 and 9 have also been analyzed in human sperm nuclei by multicolor FISH. Unfortunately, this assay does not allow to determine the specific type of structural aberrations observed in sperm nuclei. An association between advancing donor age and increased frequency of numerical and structural chromosome abnormalities has been reported in spermatozoa of normal men.

Segregation of chromosomes in sperm of reciprocal translocation carriers: a review.

Reciprocal translocations, the most frequent structural aberration in humans, are mainly transmitted by one of the parents. In order to analyze the chromosomal content of the spermatozoa from carriers of chromosomal reorganizations, two methods have been used, karyotyping of sperm chromosomes by the human-hamster system and fluorescence in situ hybridization (FISH) in decondensed sperm nuclei. In this work, we review 92 sperm chromosome segregation studies from 85 different reciprocal translocation carriers, including a triple translocation carrier. Using the human-hamster method, a total of 5,818 spermatozoa from 44 reciprocal translocation carriers have been analyzed, 43 of them carrying a single reciprocal translocation and one was a carrier of a double reciprocal translocation. A segregation analysis in a carrier of a t(2;22;11) has been also reported. Carrying out FISH in sperm nuclei, a total of 237,042 spermatozoa from 46 reciprocal translocation carriers have been analyzed. Six of these were also analyzed by the human-hamster system. Taking into account both methods, a total of 76 different reciprocal translocations have been studied. In 74 of these 76 translocations, the reorganization occurs between autosomes, and in the other two, the Y chromosome is involved. Although along general lines, there are similarities between the results obtained by the two methods of analysis, variations are observed when the distribution of the different types of segregations that produce imbalances is compared. As a general rule reciprocal translocation carriers produce more unbalanced sperm than normal or balanced sperm. The results reported also corroborate that the proportion of unbalanced forms depends on the characteristics of the reorganization and that it varies widely. Thus the importance of performing a detailed meiotic behavior analysis for each particular translocation in order to obtain enough information to give adequate genetic counseling is stressed. Aspects as to the possible overestimation of 3:1 segregations or the presence of interchromosomal effects still need to be elucidated.

Meiotic abnormalities in infertile males.

Meiotic anomalies, as reviewed here, are synaptic chromosome abnormalities, limited to germ cells that cannot be detected through the study of the karyotype. Although the importance of synaptic errors has been underestimated for many years, their presence is related to many cases of human male infertility. Synaptic anomalies can be studied by immunostaining of synaptonemal complexes (SCs), but in this case their frequency is probably underestimated due to the phenomenon of synaptic adjustment. They can also be studied in classic meiotic preparations, which, from a clinical point of view, is still the best approach, especially if multiplex fluorescence in situ hybridization is at hand to solve difficult cases. Sperm chromosome FISH studies also provide indirect evidence of their presence. Synaptic anomalies can affect the rate of recombination of all bivalents, produce achiasmate small univalents, partially achiasmate medium-sized or large bivalents, or affect all bivalents in the cell. The frequency is variable, interindividually and intraindividually. The baseline incidence of synaptic anomalies is 6-8%, which may be increased to 17.6% in males with a severe oligozoospermia, and to 27% in normozoospermic males with one or more previous IVF failures. The clinical consequences are the production of abnormal spermatozoa that will produce a higher number of chromosomally abnormal embryos. The indications for a meiotic study in testicular biopsy are provided.

Cytogenetic analysis of sperm chromosomes and sperm nuclei in a male heterozygous for a reciprocal translocation t(5;7)(q21;q32) by in situ hybridisation.

We have studied the meiotic segregation of a reciprocal translocation t(5;7)(q21;q32) in a male carrier, using the human sperm-hamster oocyte fusion technique and the whole chromosome painting. A total of 296 sperm complements were analysed by dual chromosome painting. The frequencies of alternate, adjacent-1, adjacent-2 and 3:1 segregation were 49.7%, 32.4%, 16.2% and 1.7% respectively. Aneuploidy frequencies for chromosomes not involved in the translocation were determined by FISH on decondensed sperm heads using probes from chromosomes X, Y, 6, 18 and 21. A total of 20,118 spermatozoa was analysed, 10,201 by two-colour FISH (probes for chromosomes 6 and 21) and 9917 by three-colour FISH (probes for chromosomes X, Y, and 18). There was no evidence of an interchromosomal effect, since disomy frequencies were within the range of normal controls.

Meiotic segregation analysis in a t(4;8) carrier: comparison of FISH methods on sperm chromosome metaphases and interphase sperm nuclei.

Meiotic segregation of a t(4;8)(q28;p23) translocation carrier was determined by two different methods to compare the final results. A total of 352 sperm chromosome complements, obtained after human-hamster in vitro fertilisation, were analysed by whole chromosome painting, and 6590 sperm heads were studied by fluorescence in situ hybridisation (FISH). Frequencies of alternate, adjacent I, adjacent II and 3 : 1 segregations were, for sperm chromosomes, 35.5, 33.2, 19.9 and 11.3% respectively. For sperm head analysis, results were 30.5, 28.5, 20.5 and 19.5% respectively. There were no statistically significant differences between the two methods with respect to the observed frequencies of sperm with balanced and unbalanced chromosome constitutions. Among unbalanced gametes, the methods differed only in the frequency of 3 : 1 segregation (chi(2), P<0.0001). Different factors that could explain this result are discussed. To determine possible interchromosomal effects, multicolour FISH was used on sperm heads. Disomy rates of sex and 18 chromosomes were higher in the translocation carrier than in the control. The differences observed were statistically significant (P<0.0001 for chromosomes X and 18, and P=0.0091 for chromosome Y).

The use of a cell-cycle phase-marker may decrease the percentage of errors when using FISH in PGD.

Fluorescent DNA probes are used to characterise the chromosome constitution of preimplantation embryos. FISH is used to select normal or balanced embryos in carriers of balanced chromosomal rearrangements, for embryo sexing or for aneuploidy screening in women of advanced age, who have had recurrent abortions or IVF failures. In most cases, FISH is performed on interphase blastomeres which are asynchronously dividing cells, that can be in G1, S or G2. However, a correct interpretation of a double FISH signal, which may correspond to a split signal, to a replicated chromosome region or to the presence of an extra chromosome is essential to establish an accurate diagnosis. To determine if the cell stage could influence the interpretation of FISH results, we compared the signal characteristics of one locus-specific probe, two different subtelomere region probes, and a centromere region probe in non-dividing Sertoli cells and in proliferating lymphocytes. Most cells had two signals per chromosome pair (i.e., a situation corresponding to G0 in Sertoli cells and to G1 or to a prereplication stage in lymphocytes). Nevertheless, in proliferating cells the percentage of nuclei with a number of signals different from the expected (two unreplicated chromosomes per pair) was different from that found in non-dividing cells (P < 0.05). It was estimated that 10.8% of double dots in dividing cells resulted from DNA replication. The sequence of replication was first the locus-specific region, second a telomere region, and third the centromere. In conclusion, the DNA replication process could result in errors of interpretation (misdiagnosis) in 7% of proliferating cells. Thus, the use of a cell cycle phase-specific marker could avoid errors by indicating the cell stage in which the nucleus analysed is found.

Characterization of all human male synaptonemal complexes by subtelomere multiplex-FISH.

During meiotic prophase I, homologous chromosomes synapse and recombine. Both events are of vital importance for the success of meiosis. When homologous chromosomes synapse, a proteinaceous structure called synaptonemal complex (SC) appears along the pairing axis and meiotic recombination takes place. The existence of immunolabeling techniques for SC proteins (SCP1, SCP2 and SCP3) and for DNA mismatch repair proteins present in late recombination nodules (MLH1) allow analyses of both synapsis and meiotic recombination in the gametocyte I. In situ hybridization methods can be applied afterwards because chromatin is preserved during cell fixation for immunoanalysis. The combination of both methodologies allows the analysis of synapsis and the creation of recombination maps for each bivalent. In this work we apply the seven-fluorochrome subtelomere-specific multiplex FISH assay (stM-FISH) to human male meiotic cells previously labeled by immunofluorescence (SCP1, SCP3, MLH1, CENP) to assess its utility for human SC karyotyping. This FISH method consists of microdissected subtelomeric probes labeled combinatorially with seven different fluorochromes. Results prove its usefulness for the identification of all human SCs. Furthermore, by labeling subtelomeric regions this one-single-step method enables the characterization of interstitial and terminal SC fragments and SC delineation even if superposition is present in pachytene spreads.